Phosphorus-containing zeolite catalyst

ABSTRACT

A zeolite catalyst is prepared by treating a zeolite with a phosphorus compound to form a phosphorus-treated zeolite. The phosphorus-treated zeolite is heated to a temperature of about 300° C. or higher and combined with an inorganic oxide binder material to form a zeolite-binder mixture. The zeolite-binder mixture is heated to a temperature of about 400° C. or higher to form a bound zeolite catalyst. The bound zeolite may exhibit at least two  31 P MAS NMR peaks with maxima at from about 0 to about −55 ppm, with at least one peak having a maximum at from about −40 to about −50 ppm. Zeolites containing 10-oxygen ring pores that have been prepared in such a way may be used in aromatic alkylation by contacting the bound zeolite catalyst with an aromatic alkylation feed of an aromatic compound and an alkylating agent under reaction conditions suitable for aromatic alkylation.

This application is a division of U.S. patent application Ser. No.11/195,970, entitled “Zeolite Catalyst and Method of Preparing and Useof Zeolite Catalyst,” filed Aug. 3, 2005 now U.S. Pat. No. 7,368,410,which is herein incorporated by reference in its entirety.

TECHNICAL FIELD

The invention relates generally to the alkylation of aromatic compoundsand catalysts used for such reactions and their preparation.

BACKGROUND

Para-xylene is a valuable substituted aromatic compound because of itsgreat demand for its oxidation to terephthalic acid, a major componentin forming polyester fibers and resins. It can be commercially producedfrom hydrotreating of naphtha (catalytic reforming), steam cracking ofnaphtha or gas oil, and toluene disproportionation.

Alkylation of toluene with methanol, which is also known as toluenemethylation, has been used in laboratory studies to produce para-xylene.Toluene methylation has been known to occur over acidic catalyst,particularly over zeolite or zeolite-type catalyst. In particular,ZSM-5-type zeolite, zeolite Beta and silicaaluminophosphate (SAPO)catalysts have been used for this process. Generally, a thermodynamicequilibrium mixture of ortho (o)-, meta (m)- and para (p)-xylenes can beformed from the methylation of toluene, as is illustrated by thereaction below.

Thermodynamic equilibrium compositions of o-, m-, and p-xylenes may bearound 25, 50 and 25 mole %, respectively, at a reaction temperature ofabout 500° C. Such toluene methylation may occur over a wide range oftemperatures, however. Byproducts such as C9+ and other aromaticproducts can be produced by secondary alkylation of the xylene product.

Para-xylene can be separated from mixed xylenes by a cycle of adsorptionand isomerization. Such cycle may have to be repeated several timesbecause of the low isomeric concentration in the equilibrium mixture. Ahigh purity grade (99+%) p-xylene is desirable for its oxidation toterephthalic acid. The production cost for such a high purity gradep-xylene can be very high, however. A different method that employscrystallization techniques can be used and may be less expensive wherethe concentration of p-xylene is around 80% or higher in the initialxylene product. Thus, higher than equilibrium concentrations of p-xylenemay be desirable.

A significantly higher amount of p-xylene can be obtained in toluenemethylation reaction if the catalyst has shape selective properties.Shape selective properties can be obtained in modified zeolite catalystsby narrowing zeolite pore opening size, inactivation of the externalsurface of the zeolite or controlling zeolite acidity. Toluenemethylation may occur over modified ZSM-5 or ZSM-5-type zeolite catalystgiving xylene products containing significantly greater amounts ofp-xylene than the thermodynamic concentration.

Unfortunately, there are a number of technical hurdles for toluenemethylation to be commercially successful and improvements are needed.Among these are fast catalyst deactivation and low methanol selectivity.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying figures, in which:

FIG. 1 shows ³¹P MAS-NMR spectrum for phosphorus-modified ZSM-5 zeoliteCatalyst A;

FIG. 2 shows ³¹P MAS-NMR spectra for Catalysts I (spectrum a) and K(spectrum b);

FIG. 3 shows ³¹P MAS-NMR spectra for a phosphorus-modified ZSM-5 zeolite(spectrum a) precursor used for preparing Catalysts L and M, and for analumina bound phosphorus-modified ZSM-5 zeolite—Catalyst M (spectrum b);

FIG. 4 is a plot of toluene conversion over time for the toluenemethylation reaction for Catalyst L of Example 14;

FIG. 5 is a plot of methanol selectivity (curve 1), mixed-xyleneselectivity (curve 2) and p-xylene selectivity (curve 3) over time forthe toluene methylation reaction for Catalyst L of Example 14;

FIG. 6 is a plot of toluene conversion over time for the toluenemethylation reaction for Catalyst M of Example 15;

FIG. 7 is a plot of methanol selectivity (curve 1), mixed-xyleneselectivity (curve 2) and p-xylene selectivity (curve 3) over time forthe toluene methylation reaction for Catalyst M of Example 15; and

FIG. 8 is a plot of toluene conversion over time for the toluenemethylation reaction for Catalyst A of Example 16.

DETAILED DESCRIPTION

ZSM-5 zeolite is one of the most versatile catalysts used in hydrocarbonconversions. It is a porous material containing intersectingtwo-dimensional pore structure with 10-membered oxygen rings. Zeolitematerials with such 10-membered oxygen ring pore structures are oftenclassified as medium-pore zeolites. Modification of ZSM-5-type zeolitecatalysts with phosphorus-containing compounds has been shown to provideshape selective properties to the catalyst, yielding significantlygreater amounts of p-xylene than the thermodynamic equilibrium valuewhen used in toluene methylation compared to unmodified catalysts. Suchmodification has been shown to provide selectivity for p-xylenes ofgreater than 80%. Although such phosphorus-treated ZSM-5 catalysts mayhave a high selectivity for p-xylene, they tend to deactivate at a veryfast rate; for example, the catalyst may lose greater than 50% of itsinitial activity within a day. This may possibly be due to cokedeposition on the catalyst.

As used herein, the expression “ZSM-5-type” is meant to refer to thosezeolites that are isostructurally the same as ZSM-5 zeolites.Additionally, the expressions “ZSM-5” and “ZSM-5-type” may also be usedherein interchangeably to encompass one another and should not beconstrued in a limiting sense. As used herein, catalytic activity can beexpressed as the % moles of the toluene converted with respect to themoles of toluene fed and can be defined by the following formulas:Mole % Toluene Conversion=[(T _(i) −T _(o))/T _(i)]×100  (2)where, T_(i) is the number of moles of toluene fed and T_(o) is thenumber of moles toluene unreacted. As used herein, selectivity for mixedxylenes may be expressed as:Mole % Mixed Xylene Selectivity=[X _(tx)/(T _(i) −T _(o))]×100  (3)where, X_(tx) is the number of moles of mixed (o-, m- or p-) xylenes inthe product. As used herein, selectivity for p-xylene may be expressedas:Mole % p-Xylene Selectivity=(X _(p) /X _(tx))×100  (4)where, X_(p) is the number of moles of p-xylene.As used herein, methanol conversion may be expressed as:Mole % Methanol Conversion=[(M _(i) −M _(o))/M _(i)]×100  (5)where, M_(i) is the number of moles of methanol fed and M_(o) is thenumber of moles methanol unreacted.As used herein, methanol selectivity for toluene methylation may beexpressed as:Mole % Methanol Selectivity=[X _(tx)/(M _(i) −M _(o))]×100  (6)where, X_(tx) is the number of moles of mixed (o-, m- or p-) xylenes,M_(i) is the number of moles of methanol fed and M_(o) is the number ofmoles of unreacted methanol.

The ZSM-5 zeolite catalysts and their preparation are described in U.S.Pat. No. 3,702,886, which is herein incorporated by reference. In thepresent invention, the ZSM-5 zeolite catalyst may include those having asilica/alumina molar ratio of 200 or higher, more particularly fromabout 250 to about 500 prior to modification. The starting ZSM-5 may bean NH₄ ⁺ or H⁺ form and may contain traces of other cations.

The ZSM-5 may be modified by treating with phosphorus-containingcompounds. Such phosphorus-containing compounds may include, but are notlimited to, phosphonic, phosphinous, phosphorus and phosphoric acids,salts and esters of such acids and phosphorous halides. In particular,phosphoric acid (H₃PO₄) and ammonium hydrogen phosphate ((NH₄)₂HPO₄) maybe used as the phosphorus-containing compound to provide a catalyst fortoluene methylation with shape selective properties to provide increasedp-xylene selectivity. Such modified catalysts may contain phosphorus (P)in an amount of from about 0.01 to about 0.15 g P/g zeolite, moreparticularly from about 0.02 to about 0.13 g P/g zeolite, and moreparticularly from about 0.07 g P/g zeolite to about 0.12 g P/g zeolite,and still more particularly from about 0.09 g P/g zeolite to about 0.11g P/g zeolite. After phosphorus treatment, the phosphorus-treatedzeolite may be dried.

It has been discovered that increased para-selectivity may be achievedin aromatic alkylation, particularly for toluene alkylation, when theP-modified zeolite is heated at 300° C. or higher after phosphorustreatment, and is then subsequently bound with a suitable binder, as isdiscussed later on. This heating may result in the formation of variousphosphorus species within the zeolite. Such heating may also facilitatedrying of the catalyst after the phosphorus treatment. Temperatures of300° C., 400° C. or more are particularly useful in providing suchincreased para-selectivity. A suitable range for such heating subsequentto phosphorus treatment is from about 300° C. to about 600° C. Suchheating may be carried out for 0.5 hour or more.

It has been further discovered that combining the P-treated ZSM-5(P/ZSM-5) with a suitable binder after the initial heating step, asdiscussed above, may further increase product selectivity in aromaticalkylation. In particular, the P/ZSM-5 when heated and then bound with asuitable binder the catalyst may provide an increased selectivity forpara-xylene by at least 5% compared to the same catalyst unbound whenused in toluene methylation under similar conditions. Suitable bindermaterials may include inorganic oxide materials. Examples of suchmaterials include alumina, clay, aluminum phosphate and silica-alumina.In particular, a binder of alumina or clay or their combinations areparticularly useful. The bound catalyst may contain from about 1% toabout 99% by total weight of bound catalyst, more particularly fromabout 10% to about 50% binder by total weight of bound catalyst.

To form the bound catalyst, the binder material may be combined with thephosphorus-treated zeolite to form an extrudable mixture. The P-treatedzeolite bound with the binder may be calcined or heated at a temperatureof 400° C. or higher, more particularly at a temperature between 500° C.and 700° C. Such heating may be carried out for 0.5 hours or more toform the bound catalyst. It has been discovered that heating theP-treated ZSM-5 at a temperature of about 300° C. or higher and thenbinding the zeolite with a suitable binder, as described herein, mayresult in the bound zeolite exhibiting multiple P-species, as shown by³¹P MAS NMR peaks.

In particular, the bound zeolite catalyst may exhibit at least two peakshaving maxima at from about 0 ppm to about −55 ppm. More particularly,the bound zeolite catalyst may exhibit a ³¹P MAS NMR peak having amaximum at from about 0 ppm to about −25 ppm, more particularly at fromabout −5 ppm to about −20 ppm, and another with a maximum at from about−40 ppm to about −50 ppm. Such peaks are an indication of variousphosphorus species. In particular, a ³¹P MAS NMR peak with maximum ofabout −44 ppm may be indicative of polyphosphate species. A peak with amaximum at from about 0 ppm to about −25 ppm may be indicative ofphosphorus bound by extra-framework aluminum or amorphous alumina.Aluminophosphates (AlPO₄) and silicoaluminophosphates (SAPO) may beindicated by a peak with a maximum at around −28 ppm to about −35 ppm.Free phosphates may be indicated by a peak with a maximum at around 0ppm.

This is in contrast to a bound P-modified zeolite catalyst that has beencalcined or heated at the same temperature, but where the unboundP-modified zeolite precursor has not undergone heating at a temperatureof 300° C. or more. Such bound P-modified zeolite catalysts have beenshown to exhibit only a single ³¹P MAS NMR peak. This indicates adifference in the interaction between the binder and the phosphorusspecies that is dependent upon the heating temperature of the unboundP-modified zeolite precursor.

The P-modified ZSM-5 catalyst, bound or unbound, may be mildly steamedat a temperature of 300° C. or lower before using the catalyst in anyreaction. The steaming can be carried out in-situ or ex-situ of thereactor. The use of catalyst steaming at mild temperatures is describedin co-pending U.S. patent application Ser. No. 11/122,919, filed May 5,2005, entitled “Hydrothermal Treatment of Phosphorus-Modified ZeoliteCatalysts,” which is herein incorporated by reference.

The P-modified ZSM-5 catalyst, bound or unbound, may be contacted withan appropriate feed of an aromatic hydrocarbon and an alkylating agentunder alkylation reaction conditions to carry out aromatic alkylation.The catalyst has particular application for use in toluene methylationutilizing a toluene/methanol feed. A gas cofeed may also be used. Thecofeed gas may include hydrogen or an inert gas. As used herein, theexpression “alklyation feed” is meant to encompass the aromatic compoundand the alkylating agent. As used herein, the expression “methylationfeed” is meant to encompass the feed of toluene and methanol.

In addition to any cofeed gas, water that may be in the form of steam,may also be introduced into the reactor as cofeed along with thealkylation feed. The water or steam used for the methylation reactionmay be introduced with or without hydrogen or inert gas as cofeed withthe alkylation feed to the reactor during the start up of the alkylationreaction, or it may be introduced subsequent to initial start up. Ineither case, liquid water may be added and vaporized prior to its mixingwith cofeed gas (if any) and the alkylation feed. The use of watercofeed is described in U.S. Patent App. Publication No. US2005/0070749A1, published Mar. 31, 2005, and entitled “Toluene Methylation Process,”which is herein incorporated by reference.

The reactor pressure for toluene methylation or other aromaticalkylation may vary, but typically ranges from about 10 to about 1000psig. Reactor temperatures may vary, but typically range from about 400to about 700° C. Upon introduction of feed into the reactor, thecatalyst bed temperature may be adjusted to a selected reactiontemperature to effect a desired conversion. The temperature may beincreased gradually at a rate of from about 1° C./min to about 10°C./min to provide the desired final reactor temperature. As used in theexamples, reactor temperature refers to the temperature as measured atthe inlet of catalyst bed of the reactor.

The reaction may be carried out in a variety of different reactors thatare commonly used for carrying out aromatic alkylation reactions. Singleor multiple reactors in series and/or parallel are suitable for carryingout the aromatic alkylation.

The P-modified ZSM-5 zeolite catalyst, as described herein, hasparticular application for use in toluene methylation for preparing axylene product from a feed of toluene and methanol. The catalystprovides increased selectivity for p-xylene when used in toluenemethylation. In particular, the catalyst may provide greater than 85%,90% or 95% para-xylene selectivity when used in toluene methylation.Additionally, in certain instances, greater than 95% of total xyleneselectivity may be achieved.

Additionally, the P/ZSM-5 catalyst described herein, bound or unbound,may provide steady catalyst activity and selectivity for toluenemethylation over periods of 25 days, 30 days, 60 days or more underappropriate reaction conditions. In carrying out such reactions forsteady catalyst performance, the catalyst may be contacted with amethylation feed and gas cofeed at a suitable temperature to give adesired toluene conversion. In the examples discussed below, the desiredtoluene conversion was 63% of theoretical maximum toluene conversionusing a methylation feed containing a toluene/methanol molar ratio ofabout 4.5. The reaction was carried out at a constant reactortemperature over the test period.

The following examples better serve to illustrate the invention.

EXAMPLES

Catalyst A

A binder-free, P-modified ZSM-5 (P/ZSM-5) was prepared. The startingzeolite powder was an NH₄-ZSM-5 powder having SiO₂/Al₂O₃ mole ratio of280. A slurry containing 700 g of NH₄-ZSM-5 zeolite and 700 ml of waterwas prepared in a 2-L beaker. The beaker was placed on a hot plate andthe zeolite slurry was stirred using a mechanical (overhead) stirrerwith 250-300 rpm. The temperature of the slurry was slowly raised toabout 80-85° C. A phosphoric acid solution containing 319 g ofphosphoric acid (Aldrich, 85 wt % in aqueous) was slowly added to theslurry. The slurry temperature was further increased to between 95-100°C. and heating was continued until all liquid was evaporated. Thephosphoric-acid modified zeolite was then heated in a convection oven inair at the following temperature program: 90° C. to 120° C. for threehours, at 340° C. to 360° C. for three hours and at 510° C. to 530° C.under air for 10 hours. The resulting heat-treated zeolite (Catalyst A)was then crushed and sized using 20 and 40 mesh screens for catalyticreaction or sieved through 80 mesh screen for binding the zeolite with abinder.

Catalyst A was analyzed for Si, Al and P by X-ray fluorescence (XRF),and for BET surface area and total pore volume by N₂ adsorption. Asshown in Table 1, Catalyst A contained 35.73 wt % Si, 0.28 wt % Al and9.01 wt % P, and had a BET surface area of 160 m²/g and total porevolume of 0.12 ml/g. The X-ray diffraction pattern for Catalyst A wasrecorded on a Philips (X'Pert model) diffractometer over a range of5-55° at a scan rate 2° per minute using CuKα1 radiation. The resultsare presented in Table 2.

TABLE 1 Elemental Analysis, wt % N₂ Adsorption Si Al P SA, m²/g PV, ml/g³¹P MAS NMR 35.73 0.28 9.01 160 0.12 See spectrum FIG. 1

TABLE 2 Powder XRD Intensity* d-spacing [A] Intensity 11.09 100 10.00 559.88 42 9.68 17 8.02 8 6.68 7 6.33 8 5.98 16 5.69 7 5.56 9 4.25 9 4.00 63.84 50 3.81 31 3.71 27 3.64 10 3.52 22 2.98 8 2.78 5 *Intensities shownare scaled in arbitrary units so that most intense peak is 100.

Solid state Magic Angle Spinning (MAS) NMR spectra were recorded onCatalyst A with 400 MHz spectrometer (²⁷Al at 104.5 MHz) at roomtemperature (²⁷Al MAS NMR). Samples were packed in silicon nitriderotors (Si₃N₄) and spun at 13 to KHz sample spinning (about 800000 rpm).A 10 degree tip and recycle delay of 0.5 s were used to avoidsaturation. About 4000 to 10000 scans were accumulated to signal averageand improve signal/noise ratio. Proton decoupling was not employed. Allspectra were referenced to aluminum chloride hexahydrate (run separatelyin a tube) at 0.0 ppm on the chemical shift scale. This leads to aninternal reference of 104.85 ppm on the aluminum nitride (small impurityin the silicon nitride rotors) peak. The Catalyst A sample shows a weakpeak at 55-50 ppm region assigned to structural tetrahedral aluminum.The tetrahedral aluminum peak is severely distorted, indicating thepresence of nested silanols caused by holes in the structure uponremoval of some of the framework aluminum. The adjacent peak (30-40 ppm)peak is due to severely distorted but still in the framework aluminumatoms probably either in the 3 or 5 coordination with oxygens. Thebiggest peak in the spectrum at −14 ppm is from octahedrally coordinatedaluminum atoms that are formed when tetrahedrally coordinated frameworkaluminum is removed from the zeolite framework by the phosphatemodification process as mentioned above.

Solid state Magic Angle Spinning (MAS) NMR spectra were recorded onCatalyst A with 400 MHz spectrometer (³¹P at 161.7 MHz) at roomtemperature (³¹P MAS NMR). Samples were packed in silicon nitride rotors(Si₃N₄) and spun at 13 to KHz sample spinning (about 800000 rpm). A 30degree tip and recycle delay of 15 s were used to avoid saturation.About 4000 to 10000 scans were accumulated to signal average and improvesignal/noise ratio. Proton decoupling was not employed. All spectra weredoubly referenced to tetramethyl diphosphine disulphide at 37.8 ppm and85% phosphoric acid (run separately in a tube) at 0.0 ppm on thechemical shift scale.

FIG. 1 illustrates ³¹P MAS NMR spectrum for a P/ZSM-5 zeolite (CatalystA). The ³¹P MAS NMR spectrum for Catalyst A shows peaks at 0, −11, −31and −44 ppm attributed to various P-species such as free phosphorus andphosphorus bonded (via oxygen) to Si and Al.

Catalyst B

Heat-treated, P-modified ZSM-5 (described as Catalyst A earlier) wasbound with 20 wt % alumina binder. 19.18 gm of alumina (pseudobohemitetype, available from Alcoa, HiQ-40 grade) was peptized with mineral acid(e.g., HNO₃) and then mixed with 57.44 gm of P/ZSM-5 zeolite powder (80mesh). Water was spray added to make a soft paste. The catalyst pastewas calcined or heated (as irregular chunks or formed in a cylindricalshape) at 510° C. to 530° C. using the same temperature profile asdescribed for Catalyst A above. The resulting Catalyst B was crushed andsized using 20 and 40 mesh screens for catalytic test.

Catalyst C

Heat-treated, P-modified ZSM-5 (earlier described as Catalyst A) wasbound with 20% silica binder. 8.19 gm of Aerosil-200 was mixed with 5.05gm of Ludox-HS-40 (Colloidal Silica) in which 20.0 ml of 0.2 N NH₄OH wasadded slowly with stirring. 20.02 gm of P/ZSM-5 powder (80 mesh) wasadded to the silica mixture and stirred well. Water was sprayed to makesoft paste and the paste was calcined at 510° C. to 530° C. using thesame temperature profile as described for catalyst A above. Theresulting Catalyst C was crushed and sized using 20 and 40 mesh screensfor catalytic tests.

Catalyst D

Catalyst A was bound with 20% aluminum phosphate. Catalyst A was boundwith aluminum phosphate, available from Aldrich Chemicals, as a binderfollowing the same procedure as described for Catalyst B. The resultingCatalyst D was crushed and sized using 20 and 40 mesh screens forcatalytic test.

Catalyst E

Catalyst A was bound with 20% kaolin. P/ZSM-5 was bound with kaolin asbinder following the same procedure as described for Catalyst B. Kaolin(aluminum silicate hydroxide), available from Aldrich Chemicals, wasused. The resulting Catalyst E was crushed and sized using 20 and 40mesh screens for catalytic test.

Examples 1-5

In Examples 1-5, Catalysts A-E were used in toluene methylation. Thereactions were each carried out in a fixed bed, continuous flow typereactor. In each case, a catalyst charge of 5.4 ml (catalyst size: 20-40mesh) was loaded in the reactor. The catalyst was dried by slowlyraising the catalyst bed temperature (about 5° C./min) to 200° C. underhydrogen flow (50 cc/min) for at least one hour. The catalyst wassteamed by introducing water vapor (2.2 mmole/min) with a carrier gas ofH₂ (459 cc/min) at 200° C. overnight. A premixed toluene and methanolfeed (molar ratio 4.5) was added to the reactor at 200° C. and thecatalyst bed inlet temperature was increased to about 550° C. The liquidhourly space velocity (LHSV) (based on methylation feed) was maintainedat about 2 hr⁻¹ and a cofeed H₂ gas was fed and maintained to provide aH₂/methylation feed molar ratio of about 7-8. In addition, water wasadded to the reactor as cofeed and was vaporized prior to introductionto the reactor. The H₂O/methylation feed molar ratio was about 0.8 andthe reactor pressure was about 20 psig. Reactor streams were analyzed tocalculate conversion and selectivity. Liquid product stream analyses andconversion and selectivity for toluene methylation reaction overCatalysts A-E are shown in Table 3 below.

TABLE 3 Catalyst A B C D E EXAMPLE 1 2 3 4 5 Time on Stream, h 28 118 24125 22 124 30 150 25 131 Product Analysis, wt % Water 20.6 20.3 20.921.5 19.2 18.8 19.3 19.2 20.2 19.6 Methanol 0.3 0.3 0.1 0.2 1.2 1.1 1.10.9 0.7 0.6 Dimethylether 0 0 0 0 0 0 0 0 0 0 Benzene 0 0 0 0 0 0 0 0 00 Toluene 64.4 64.8 65.2 64.9 76.2 76.8 76.5 76.0 69.9 69.5 Ethylbenzene0 0 0 0 0 0 0 0 0 0 p-Xylene 12.7 12.6 13.3 12.8 2.8 2.7 2.9 3.6 8.3 9.4m-Xylene 0.9 0.9 0.2 0.2 0.3 0.2 0.1 0.1 0.4 0.4 o-Xylene 0.5 0.5 0.10.1 0.2 0.2 0.1 0.1 0.2 0.2 Ethyltoluenes 0.1 0.1 0.1 0.1 0 0 0 0 0 0Trimethylbenzenes 0.4 0.4 0.1 0.1 0.1 0.1 0 0 0.2 0.2 C10+ 0 0 0 0 0 0 00 0 0 Conversion/Selectivity, mole % Toluene Conversion 15.4 14.6 14.913.6 2.6 2.0 2.8 2.7 8.7 9.7 Mixed Xylene Selectivity 97.1 97.1 98.698.6 88.5 97.5 100 100 98.1 98.2 p-Xylene Selectivity 89.6 89.6 97.797.8 84.8 86.0 93.2 94.3 93.4 94.0 Methanol Selectivity 75.6 72.3 62.964.3 29.5 24.9 27.1 27.7 58.0 61.0

Examples 6-8

Catalyst F-H

Using the procedure described for Catalyst A, NH₄-ZSM-5 having aSiO₂/Al₂O₃ molar ratio of 280 was treated with H₃PO₄ acid. The H₃PO₄acid treated ZSM-5 was then heated at 510-530° C. for approximately 10hrs. Three alumina bound catalysts were made using the resulting P/ZSM-5powder with 10 wt % alumina (Alcoa HiQ40) as binder and each was furthercalcined or heated at different maximum temperatures to form CatalystsF-H, Catalyst F was heated at a maximum temperature of 400° C. CatalystG was heated at a maximum temperature of 510° C. Catalyst H was heatedat a maximum temperature of 600° C. The catalysts were tested fortoluene methylation using the conditions described in Examples 1-5.Table 4 shows the liquid product stream analysis and conversion andselectivity for Catalysts F-H for Examples 6-8.

TABLE 4 Catalyst F G H EXAMPLE 6 7 8 Time on Stream, h 24 143 23 125 24120 Product Analysis, wt % Water 21.0 21.5 21.0 20.8 21.1 20.5 Methanol0.1 0.1 0.1 0.2 0.1 0.2 Dimethylether 0 0 0 0 0 0 Benzene 0 0 0 0 0 0Toluene 64.6 63.5 65.2 65.6 65.1 65.9 Ethylbenzene 0 0 0 0 0 0 p-Xylene13.7 14.2 12.8 12.6 13.2 13.0 m-Xylene 0.3 0.3 0.4 0.4 0.2 0.2 o-Xylene0.2 0.2 0.2 0.2 0.1 0.1 Ethyltoluenes 0.1 0.1 0.1 0.1 0.1 0.1Trimethylbenzenes 0.2 0.2 0.2 0.2 0.1 0.1 C10+ 0 0 0 0 0 0Conversion/Selectivity, mole % Toluene Conversion 14.7 14.7 13.8 13.413.4 13.4 Mixed Xylene Selectivity 98.3 98.2 98.2 98.2 98.6 98.5p-Xylene Selectivity 96.9 96.9 95.7 95.8 98.2 98.2 Methanol Selectivity65.6 65.8 64.0 63.4 60.7 64.4

Examples 9-11

Catalysts I-K

Using the procedure described for Catalyst A, NH₄-ZSM-5 having aSiO₂/Al₂O₃ molar ratio of 280 was treated with H₃PO₄ acid. The H₃PO₄acid treated ZSM-5 was then heated at different temperatures of 90° C.,250° C. or 320° C. The heat-treated, P-modified ZSM-5 zeolite powder wasthen combined with 20 wt % alumina (Alcoa HiQ40) following the sameprocedure described for Catalyst B, and was calcined or heated at amaximum temperature of from 510 to 530° C. These bound catalysts,designated as Catalysts I, J and K, were tested for toluene methylationusing the conditions described for Examples 1-5. The ³¹P MAS NMR spectrafor Catalysts I and K are shown in FIG. 2. The ³¹P MAS NMR spectrum forCatalyst I shows only a single peak at around −30 ppm with a long tail(FIG. 2 spectrum a). As the heating temperature is increased for theP/ZSM-5 (used prior to binding with alumina) to about 300° C. or higher,the final bound catalyst may show additional peak(s), including a peakat around −44 ppm (see, for example, spectrum b of FIG. 2 and spectrum bof FIG. 3). Table 5 summarizes the initial heating temperature of theunbound P/ZSM-5 and catalytic test results obtained for bound CatalystsI-K. Also, the data for Catalyst B reproduced from Table 3 is presentedin Table 5 for comparison. Those catalysts made from the P-modifiedZSM-5 zeolite that were heated at a temperature of 300° C. or higher andthen bound with a suitable binder showed 90% or higher p-xyleneselectivity for toluene methylation.

TABLE 5 Catalyst I J K B P/ZSM-5 Heating Temp¹ 90° C. 250° C. 320° C.520° C. EXAMPLE 9 10 12 2 Time on 23 126 54 150 24 126 24 125 Stream, hProduct Analysis, wt % Water 21.0 21.0 20.9 21.7 21.1 21.6 20.9 21.5Methanol 0 0 0 0 0 0 0.1 0.2 Dimethyl- 0 0 0 0 0 0 0 0 ether Benzene 0.30.1 0.1 0.1 0.1 0 0 0 Toluene 63.4 63.0 63.8 62.3 65.8 64.0 65.2 64.9Ethylben- 0 0 0 0 0 0 0 0 zene p-Xylene 12.1 13.3 12.5 13.1 12.7 14.013.3 12.8 m-Xylene 2.2 1.8 2.3 1.7 0.2 0.2 0.2 0.2 o-Xylene 0.8 0.7 0.10.7 0.1 0.1 0.1 0.1 Ethyl- 0 0 0 0.1 0.1 0.1 0.1 0.1 toluenes Trimethyl-0.2 0.3 0.3 0.3 0 0 0.1 0.1 benzenes C10+ 0 0 0 0 0 0 0 0Conversion/Selectivity, mole % Toluene 16.2 16.6 15.6 16.4 13.2 14.614.9 13.6 Conversion Mixed 96.7 97.7 96.4 97.2 98.6 99.2 98.6 98.6Xylene Selectivity p-Xylene 80.0 84.6 84.1 84.7 98.2 98.4 97.7 97.8Selectivity Methanol 69.7 72.1 67.9 70.8 58.3 64.6 62.9 64.3 Selectivity¹Maximum temperature at which P/ZSM-5 was heated prior to binding withalumina.

For comparison purposes, the conversion and selectivity data shown inTable 5 was averaged, and those observed for Catalyst I were scaled to1.00 and then were compared with other catalysts on a relative scale. Asshown in Table 6, with the increase of the first heating temperature ofthe phosphorus-treated ZSM-5 prior to combining the zeolite with abinder, the p-xylene selectivity increased with a decrease in tolueneconversion.

TABLE 6 Catalyst I J K B P/ZSM-5 Heating Temperature, ° C.¹ 90 250 320520 Relative Activity² 1.00 0.98 0.85 0.87 Relative Para-Selectivity²1.00 1.02 1.19 1.19 ¹Maximum temperature at which P/ZSM-5 was heatedprior to binding with alumina. ²Average of two data points shown inTable 1 and 5 for the respective catalyst. Activity and selectivityobserved on catalyst I were scaled to 1.00 and then compared with thoseobtained on other catalysts.

As can be seen, the P/ZSM-5 zeolite that was heated at a temperature ofabout 300° C. or above, and then bound with alumina followed bycalcinations or heating at 500° C. above showed increased shapeselectivity producing p-xylene selectively for toluene methylation.Higher activity with decreased p-selective catalyst can be achieved byheating the P/ZSM-5 at 300° C. or less and binding with alumina andcalcining or heating at 500° C. or higher.

Examples 12-13

Catalyst L and M

Using the procedure described for Catalyst A, an NH₄-ZSM-5 zeolite(SiO₂/Al₂O₃ mole ratio 280) was treated with H₃PO₄ and then heated at amaximum temperature of 550° C. Analyses of the P-treated ZSM-5 zeolitepowder, as was carried out for Catalyst A, are shown in Tables 7 and 8.The ³¹P MAS NMR of the P/ZSM-5 zeolite is shown in FIG. 3 (spectrum a).The P/ZSM-5 showed similar properties to those of Catalyst A. TheP/ZSM-5 zeolite was bound with 20% alumina (pseudobohemite type) andextruded to make 1/16-inch cylindrical shape catalyst. Alcoa aluminagrades HiQ-40 and HiQ-10 were used for Catalyst L and M, respectively.Catalysts L and M were calcined or heated at a maximum temperaturebetween 510° C. and 530° C. FIG. 3 shows a ³¹P MAS NMR spectrum(spectrum b) for an alumina bound catalyst—Catalyst M. The ³¹P MAS NMRspectrum for Catalyst M shows two strong peaks at around −13 ppm (broadpeak) and −44 ppm. This differs significantly from the ³¹P MAS NMRspectrum for Catalyst I, as shown in FIG. 2 (spectrum a).

TABLE 7 Elemental Analysis, wt % N2 Adsorption Si Al P SA, m2/g PV, ml/g³¹P MAS NMR 35.38 0.30 9.72 188 0.15 See spectrum a in FIG. 3

TABLE 8 Powder XRD Intensity* d-spacing [A] Intensity 11.08 100 9.99 549.89 46 9.70 17 8.01 6 6.54 7 6.33 9 5.98 16 5.70 6 5.55 8 4.25 6 4.00 73.84 57 3.80 27 3.71 28 3.64 11 3.53 18 2.98 10 2.78 6 *Intensitiesshown are scaled in arbitrary units so that most intense peak is 100.

Catalyst L and M were tested for toluene methylation. The reactor,catalyst charge, catalyst drying and steaming procedure were the same asdescribed in Examples 1-5, and the reaction conditions were the same asin Examples 1-5. Reactor liquid product stream analysis and conversionand selectivity for Catalysts L and M are shown in Tables 9 and 10,respectively. Under the reaction conditions used for toluenemethylation, Catalysts L and M showed initial 14% toluene conversion(63% of theoretical maximum) with greater than 98% mixed-xylene and 96%p-xylene selectivity.

TABLE 9 Catalyst L Example 12 Time on Stream, h 24 48 78 150 198 246 318Product Analysis, wt % Water 20.6 20.9 22.0 20.5 20.8 20.0 19.8 Methanol0 0 0.1 0.1 0.1 0.1 0.1 Dimethylether 0 0 0 0 0 0 0 Benzene 0 0 0 0 0 00 Toluene 65.5 65.1 63.9 65.9 65.6 66.1 66.4 Ethylbenzene 0 0 0 0 0 0 0p-Xylene 13.1 13.2 13.3 12.8 12.8 13.1 13.0 m-Xylene 0.4 0.4 0.4 0.3 0.30.3 0.3 o-Xylene 0.1 0.1 0.2 0.1 0.1 0.2 0.2 Ethyltoluenes 0.1 0.1 0.10.1 0.1 0.1 0.1 Trimethylbenzenes 0.1 0.1 0.2 0.2 0 0.2 0.2 C10+Conversion/Selectivity, mole % Toluene Conversion 14.0 14.2 14.3 13.313.4 13.7 13.5 Mixed Xylene 98.4 98.4 98.3 98.3 98.4 98.3 98.3Selectivity p-Xylene Selectivity 96.2 96.2 96.3 96.3 96.3 96.5 96.5Methanol Selectivity 62.3 63.1 64.7 61.8 62.0 63.0 61.8

TABLE 10 Catalyst M Example 13 Time on Stream, h 24 54 126 150 173 293313 Product Analysis, wt % Water 20.3 20.5 19.9 19.9 21.2 20.4 20.4Methanol 0.1 0.2 0.2 0.2 0.3 0.2 0.2 Dimethylether 0 0 0 0 0 0 0 Benzene0 0 0 0 0 0 0 Toluene 66.0 65.4 65.9 65.8 64.6 65.5 65.8 Ethylbenzene 00 0 0 0 0 0 p-Xylene 12.9 13.2 13.3 13.4 13.2 13.1 12.8 m-Xylene 0.3 0.30.3 0.3 0.3 0.3 0.3 o-Xylene 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Ethyltoluenes0.1 0.1 0.1 0.1 0.1 0.1 0.1 Trimethylbenzenes 0.2 0.2 0.2 0.2 0.2 0.20.2 C10+ 0 0 0 0 0 0 0 Conversion/Selectivity, mole % Toluene Conversion13.6 13.9 13.9 13.8 14.1 13.8 13.6 Mixed Xylene 98.2 98.3 98.3 98.3 98.398.3 98.3 Selectivity p-Xylene Selectivity 96.6 96.6 96.6 96.7 97.0 97.096.7 Methanol Selectivity 63.3 64.9 65.5 66.1 67.9 67.0 65.6

Example 14

Catalyst L was further tested for catalyst stability in toluenemethylation reaction. The reactor and feed conditions were the same asthose described in Examples 1-5. After drying the catalyst at 200° C.,the catalyst was steamed overnight at 200° C. A premixed toluene andmethanol feed (molar ratio 4.5) was added to the reactor at 200° C. Theliquid hourly space velocity (LHSV) (based on methylation feed) wasmaintained at about 2 hr⁻¹ and a cofeed of H₂ gas was fed and maintainedto provide a H₂/methylation feed molar ratio of about 7-8. In additionto H₂, water vapor was added to reactor as cofeed. The H₂O/methylationfeed molar ratio was about 0.8 and the reactor pressure was about 20psig. The catalyst bed inlet temperature was increased slowly to about510° C. over a period of time to give toluene conversion of about 14%,and no reactor temperature adjustment was made during the test period of637 h (26 days). Toluene conversion, and selectivities to mixed xylene,p-xylene and methanol are shown in FIGS. 4 and 5.

Example 15

Catalyst M was further employed to show stable catalytic performancesfor toluene methylation reaction. The reactor, catalyst charge, catalystdrying and steaming procedure were the same described for Examples 1-5.After drying the catalyst at 200° C., the catalyst was steamed overnightat about 200° C. A premixed toluene and methanol feed (molar ratio 4.5)was added to the reactor at 200° C. The liquid hourly space velocity(LHSV) (based on methylation feed) was maintained at about 2 hr⁻¹ and acofeed of H₂ gas was fed and maintained to provide a H₂/methylation feedmolar ratio of about 7-8. In addition to H₂, water vapor was added toreactor as cofeed. The H₂O/methylation feed molar ratio was about 0.8and reactor pressure was about 20 psig. The catalyst bed inlettemperature was increased slowly to 535° C. over a period of time togive toluene conversion of about 14%, and no further reactor temperatureadjustment was made during the test period of 1560 h (64 days). Tolueneconversion, and selectivities to mixed xylene, p-xylene and methanol areshown in FIGS. 6 and 7.

Example 16

Catalyst A was employed to test its stable activity for toluenemethylation. The reactor, feed composition, catalyst drying and steamingconditions were the same as described for Examples 1-5. After drying thecatalyst at 200° C., the catalyst was steamed overnight at 200° C. Apremixed toluene and methanol feed (molar ratio 4.5) was added to thereactor at 200° C. The liquid hourly space velocity (LHSV) (based onmethylation feed) was maintained at about 2 hr⁻¹ and a cofeed H₂ gas wasfed and maintained to provide a H₂/methylation feed molar ratio of about7-8. In addition, water was added to the reactor as cofeed and wasvaporized prior to introduction into the reactor. The H₂O/methylationfeed molar ratio was about 0.8 and the reactor pressure was about 20psig. The catalyst bed inlet temperature was slowly raised to 492° C.when a toluene conversion of about 14% was obtained and when no furtherreactor temperature adjustment was made during the test period. Reactorstreams were analyzed to calculate conversion and selectivity. FIG. 8shows steady toluene conversion as a function of time on stream. Theunbound P/ZSM-5 catalyst (Catalyst A) showed stable performance duringthe test period of 726 hours (30 days). Table 11 presents the averagetoluene conversion, methanol selectivity, mixed-xylene selectivity andp-xylene selectivity for Catalysts A, L and M. Contrasted to the unboundP/ZSM-5 (Catalyst A), the alumina bound catalysts showed at least 5%increased p-xylene selectivity.

TABLE 11 Conversion/Selectivity, Catalyst L Catalyst M Catalyst A mole %Example 14 Example 15 Example 16 Toluene Conversion 14.6 14.4 14.6Mixed-Xylene Selectivity 98.1 97.9 96.8 p-Xylene Selectivity 96.7 94.888.0 Methanol Selectivity 65.7 70.0 67.7

1. A catalyst comprising a phosphorus-containing zeolite that is boundwith an inorganic oxide binder, wherein the phosphorus-containingzeolite is heated to a temperature of about 300° C. or higher prior tocombining with the inorganic oxide binder, and wherein the bound zeoliteexhibits at least two ³¹P MAS NMR peaks with maxima at from about 0 toabout −55 ppm, with at least one peak having a maximum at from about −40to about −50 ppm.
 2. The zeolite catalyst of claim 1, wherein: at leastone of the at least two ³¹P MAS NMR peaks has a maximum at from about −8ppm to about −15 ppm and the other of the at least two ³¹P MAS NMR peakshas a maximum at from about −40 ppm to about −55 ppm.
 3. The zeolitecatalyst of claim 1, wherein: at least one of the at least two ³¹P MASNMR peaks has a maximum at about −13 ppm and the other of the at leasttwo ³¹P MAS NMR peaks has a maximum at about −44 ppm.
 4. The catalyst ofclaim 1, wherein: the binder material includes at least one of alumina,clay, aluminum phosphate and silica-alumina.
 5. The catalyst of claim 1,wherein: the binder material is an alumina-containing material.
 6. Thecatalyst of claim 1, wherein: the zeolite is a ZSM-5 zeolite.
 7. Thecatalyst of claim 1, wherein: the binder material contains from about 1%to 99% by weight alumina.
 8. The catalyst of claim 1, wherein: thebinder material is present in an amount of from about 1% to about 99% byweight of the bound zeolite catalyst.
 9. The catalyst of claim 1,wherein: the zeolite contains 10-oxygen ring pores.